The present invention relates to a TWA measuring electrocardiograph, TWA measuring method, and TWA measurement system which can measure the presence of TWA (T-wave alternans), and more particularly to a TWA measuring electrocardiograph, TWA measuring method, and TWA measurement system which can derive a Frank's vector electrocardiogram from a scalar electrocardiogram, and measure the presence of TWA from the Frank's vector electrocardiogram.
TWA appears at onset of illness such as QT prolongation syndrome, variant angina, acute myocardial ischemia, electrolyte abnormality, paroxysmal tachycardia, bradycardia, or pericardial fluid accumulation. TWA is a phenomenon in which the amplitude and polarity of the T wave appearing in an electrocardiogram are alternately changed, and an index effective to predict sudden cardiac death. TWA is not a phenomenon which can be always observed with the naked eye, and therefore its application in clinics is limited.
From the 1980s, consequently, techniques for enabling minute TWA (Microvolt TWA: MTWA) to be measured by a computer have been developed.
Examples of currently proposed techniques for measuring TWA are a measurement technique based on the MMA (Modified Moving Average) method of General Electric (GE) Company, and that based on the periodogram of Cambridge Heart (CH), Inc. which are disclosed in U.S. Pat. No. 6,668,189 and U.S. Pat. No. 5,935,082, respectively.
The measurement technique of GE Company is directed to a method of analyzing a time waveform in a time region, and is said to have resistance to noises. However, the technique does not have a long history as a measurement technique, and it is required to watch its clinical effect.
By contrast, the measurement technique of CH Inc. which is a technique in a frequency region has been used from the 1980s, and hence its effectiveness in clinics has been proved. Today, therefore, it is considered that the measurement technique based on the periodogram of CH Inc. is clinically more useful than that based on the MMA method of GE Company.
With respect to the measurement technique based on the periodogram of CH Inc., after its announcement, various techniques for performing new processes, such as a technique of measurement electrodes are added, and still now the added latest techniques have been used.
However, the measurement technique based on the periodogram of CH Inc. has several problems. For example, special measurement electrodes for eliminating noises must be used, and a Frank's vector electrocardiogram which is not necessarily commonly used must be acquired.
The use of special measurement electrodes, or the acquisition of a Frank's vector electrocardiogram imposes a burden on a measuring person because the placement of measurement electrodes and the like are different from those in the case where a usual 12-lead electrocardiogram is to be acquired. In the Frank's lead method, moreover, electrodes must be placed also on the back. Therefore, a burden is imposed also on the subject. When a usual measuring person uses the unaccustomed Frank's lead method, it is seemed that a larger measurement error caused by displacement of the attachment positions of electrodes may be produced as compared with standard lead which is prevalently employed.